This invention relates to pneumatic vehicle tires, and more specifically to valves for such tires that indicate a low pressure condition by lighting a lamp.
Tubeless tires for motor vehicles are inflated by valve stems passing through a standard size hole in the wheel rims, to which they are hermetically sealed by a resilient shouldered bushing seal that is compressed by a nut. Any device that will not permit passage of the stem through the standard hole in the rim will not be acceptable. The tires are also sealed to the rims. A valve core screws inside the stem free end, and is sealed in the stem to permit air to pass only when an inner element in the core is depressed. A cover cap screws onto an outer thread on the stem. If a tire is run without adequate pressure, it will be subject to damage, and may endanger the vehicle.
Prior art to indicate by a light signal that tire pressure is low is exemplified by U.S. Pat. Nos. 4,945,337 and 5,025,244 issued to Huang; U.S. Pat. No. 5,604,481 issued to Lin; and U.S. Pat. No. 5,856,619 issued to Wang. They include a chamber with a battery, and a light that is turned on when the pressure falls below a preset value. In every case, the chamber replaces the cover cap by screwing onto the external thread of the valve stem. There is no problem with passage through the standard hole in the rim, because they are mounted on the stem after it is in place. In order for the chamber to sense the pressure inside the tire, a protuberance at the end of the chamber presses on the inner element of the valve core, opening it. A resilient gasket seals the chamber to the end of the stem to prevent loss of tire pressure. In order to add air to the tire, the chamber must be removed. If the chamber is not replaced properly without trapping debris at the seal, or becomes partially unscrewed, or the gasket leaks, pressure may be lost. No provision is made for adjusting the light so that it is easily seen. They all emit light at the tip of the chamber considerably past the tip of the stem, where it will have limited visibility in some cases. Another problem is that the device may be stolen by simply unscrewing it.
It is accordingly an object of the invention to provide a device that will visually indicate when tire pressure is low. It is another object that the device not be easily stolen. It is another object of the invention that the device not lead to inadvertent tire pressure loss. It is yet another object of the invention that the device provide adjustment to position the light source so that it is readily seen. It is yet another object that air may be added to the tire without disturbing the hermetic seal. The low tire pressure indicator of the invention uses a tire stem without valve core that is sealed to the wheel rim. The invention includes all of the pressure sensing elements sealed to the stem to greatly reduce the dangers of theft and of inadvertent pressure leakage. A valve core is positioned at the end of the assembly where it can be accessed for adding air without disturbing hermetic sealing. A chamber containing a battery and a light emitter is connected to the stem to respond to sensing of a low tire pressure by emitting light. The chamber may be adjusted to ensure that light emitted from the side of the chamber is easily seen. It may be removed for battery testing and replacement without disturbing the seals. These and other objects, features, and advantages of the invention will become more apparent when the detailed description is studied in conjunction with the drawings in which like elements are designated by like reference characters in the various drawing figures.